<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <button>按钮</button>

  <script>
    // event e test  ie8
    // 1. 任何方式注册的任何事件，都是有事件对象的

    // 2. 事件对象是自动就存在的

    var btn = document.querySelector('button')

    // btn.onclick = function(e) {
    //   console.log(e)
    // }
    btn.addEventListener('click', function(e) {
      console.log(2222, e)
    })
    btn.addEventListener('mouseover', function(e) {
      console.log(3333, e)
    })
    btn.addEventListener('mouseout', function(e) {
      console.log(55555, e)
    })
  </script>
</body>
</html>